All Consuming Fear
by Hufflepuffle4
Summary: A tie in for Don't Let Go. Gaster is a single dad, who's simply trying to balance the stress of work, and his two young sons. When a young intern brings the Doctor an interesting project, he cannot resist the temptation of putting aside the Core to see what it is all about, estranging his sons in the process.
1. Chapter 1

**A/N: I have lost all control. A new chapter for Don't Let Go (NSFW) and for The GameKeeper's Daughter will be posted soon. My hiatus is overish, but this class im taking is REALLY time consuming. So bear with me, guys. This will be a bit more fluff than anything, but it ties into Don't Let Go, and tells other sides of the story with Sans and Gaster. Also, Gaster is speaking in Windings, we can just read it in English.**

The Royal Scientist was worried. His two young sons followed him closely to his lab near New Home, but this was the first time he had decided to go back to work since Papyrus was born. Sans was a few years older than his brother, and carried the youngest skeleton easily.

W.D. Gaster looked back, pausing as Papyrus was trying his damnedest to get out of Sans' grip. Their father chuckled, and walked towards them.

"I got it!" Sans insisted, readjusting his little brother. The older boy was very independent. Papyrus stopped squirming, and made gurgling noises at his father.

"I know." Gaster squatted down. His long, thin legs pointed outward, and he watched Sans struggle. "Are you sure you don't need a break?" Never mind the fact that they were late.

"Da! Da!" Papyrus struggled harder. Sans gave up, and passed his younger brother to his father. Gaster stood up, and took Sans' hand.

The little boy ogled the hole in the center. None of them knew how they had gotten there, nor how he had gotten the untreatable cracks in his skull. It didn't matter. He was their father, and that was that.

"Sans, don't sulk." A gentle reminder, not a scolding. Gaster didn't believe in scolding his children. Reminders, warning and punishments were better to him than shaming his children. The boy made a face.

"I'm not sulking, I just don't know why Papyrus hates me." He said. Gaster looked down at Sans. His overly large blue sweatshirt was nearly swallowing him. It had belong to their-

Gaster shook his head. He always tripped over something in his speech, but it didn't matter. It wasn't terribly important.

"Papyrus doesn't hate you. He's too young to understand hate, and if I have my way about it, he never will." The baby bones was gnawing on his favorite toy. Sans huffed. They walked into the lab, and the monsters that worked there stopped.

Gaster was not a commanding person, but his presence, intellect, and charisma required respect. No one questioned why he had two children with him, they simply waved to the boys, and went about their work. He set Sans and Papyrus in his office. It was half full of toys, and books, but Sans knew that Gaster's desk was off limits. Papyrus, well, he would take time to adjust to constantly being at work with his Dad.

Since it was his first day back to work, Gaster expected King Asgore to drop by. He was right, but not so that the King could see the progress of The Core, but to meet Papyrus. Sans loved playing with the King. He would bring sweets he picked up on the way for Sans, and would read to him or play games. His own sons had both died years before.

Gaster successfully completed more experiments, and when the time came, he found Sans fighting to stay awake, with Papyrus fast asleep on his lap. He smiled, and gently pulled Papyrus from his brother's arms. Convincing Sans to get up, he escorted them out the door.

"M-Mister G-Gaster S-sir!" A young girl called after him. He turned around, and the young reptilian was carrying a heavily wrapped package.

"What is it?" He faced the intern. Her glasses were askew on her nose, and she seemed frightened by him. "Alphys, right?"

She blushed. "Y-yes sir… It's just.. S-someone dropped this off a little while ago. Th-the note said not to o-open it wi-with your bare ha-hands…" She held it out to him, and realized as he began to chuckle that Sans was holding tightly to one arm, and Papyrus was fast asleep in the other. "I-I'm sorry!" She began a ramble. Gaster held up his centerless hand, Sans grabbing on his lab coat.

"Follow me, Alphys. I can study it at home." She turned red, and nodded. They headed towards the river person. Sans hated taking the boat, but Alphys couldn't take short cuts like he and Gaster could, so they sat on the edge of the boat. Papyrus was still fast asleep on his dad's shoulder. The River woman hummed a little song.

"The boy in blue will know more than you." She said in her sing song voice. Alphys jumped, and Gaster stared at her. "His power will grow, though it not yet known."

They arrived in Snowdin, and Gaster left the woman a smaller tip this time. He knew she was only rhyming because she enjoyed it, but that was… specific. Sans was pulling Gaster along to their house, and the other citizens waved to the small family.

They opened the door, and Gaster ushered Alphys to the kitchen. She waited as he put Papyrus to bed. Sans was seated on the couch while some mindless, and inaccurate, science program played.

"I apologize for the wait." Gaster said. Alphys looked uncomfortable. He stared at her, and gasped. He laughed at himself. "I am very sorry!" He began using sign language. "My sons can understand my language, so I forget that no one else can."

She sighed with relief. "I'm sorry I didn't speak up! I just…well, I was hoping you'd sp-speak English."

Sans leaned over, watching. The lizard woman set the strange package on the table. While he couldn't speak sign language, Sans could understand wingdings.

"I'm not sure wh-what it is, sir. They said it was some sort of artifact, but if-if we can-can't touch it-"

"Alphys, It doesn't matter. Gloves were invented for a reason." He was smiling, but being patient with her. Sans knew because he did that with him. "You and I will study this together. We will simply have to entrust the core to our coworkers." He told her. She gasped.

"Oh-n-no! Mister Gaster, I-I can't ask you to do that!"

"It was delivered to you, Alphys. You will study it with me, starting tomorrow. Now go home, and get some rest."

She left, protesting the whole way. Gaster said nothing. He ushered her out the door gently. Gaster tried not to sink against the door, knowing that Sans was watching him. Another setback, another distraction from the Core. He turned around, mustering a smile for his son.

"Come on, Sans. It's bed time." Gaster scooped him up.

"Daaaadddd!" He whined, slumping across his shoulder.

"Sans, it's late. You know you can't stay awake this late." The yawn that escaped from his son proved his point. "Besides, tomorrow you will be with Grillby. He agreed to watch you while I go to work." He had texted Grillby, at least. The silence usually meant yes.

"I want to help you!" Sans yawned again, his eyes drooping against his will. He buried his face into Gaster's chest as he carried him to his room. His father smiled softly. "I'm smart…"

"Yes you are." Gaster laid him on his bed. Sans mumbled another protest, but slipped into sleep.

The Royal scientist checked on papyrus, who was snoring away still. After shutting the door, he finally let himself deflate. There was already so much distracting him from his family, and the Core.

Oh, the Core. That was his most prized project. It would be the saving grace of the monsters, and more importantly, his boys. They would get to feel the sun on their bones like he had when he was younger. Getting up, Gaster looked at the clock. It was already past 10 PM. Ignoring his body's cry for food, he carefully unwrapped the orb.

It was red, shiny and circular. The note that Alphys spoke of fluttered onto the table. It was brief, but Gaster picked it up to read it.

 _Whatever you do, do not touch this._

Huh. He leaned against the table, pondering the note. It wasn't until he felt the awful burning that he realized he was doing exactly what the note said not to. Bones blistered even as he ran cold water over the wounds.

Whatever this thing was, it was extremely powerful.


	2. Chapter 2

**A/N: So, tis is chapter two. I should warn you guys this will get pretty dark towards the end, and I can warn you that there will be physical abuse. ALSO go check out my friend, Lyvellan Hawke. He is one of my besties, and just posted his first fanfic. Check it out!**

Three years. That's how long Gaster had been working on the stupid orb project. He hadn't learned much more than it burned like hell when it was touched, so he and Alphys handled it carefully. Sans had grown from a pouty five year into a snarky eight year old.

Over those three long years, Papyrus had grown into the loving, loud four year old he was. Nowadays, he and his brother would wander through Snowdin or Hotland while their estranged father worked. Every now and then, the king would allow the boys to stay in New Home with him.

Recently, Sans had gotten into a fight at school, so he and Papyrus were drug to work with their dad that Saturday. Sans was sulking while the boat sailed slowly. Gaster was reading over notes. He hadn't even notice the powers that had developed in Sans. He had learned t control the glowing in his eyes, now eye from the hit h took the other day.

The kid that had started a fight with him was some fish girl in the high school. They both had messed up an eye in the fight, but now they were friends. Gaster didn't care.

" _Fighting is wrong."_ He had said. _"You could have been killed."_ Sans was grounded, to say the least. Papyrus idolized the fish girl now, mainly because she thought she was so tough. His little brother scooted closer t him, his red scarf taking up most of his face.

"Sans." Papyrus nudged him. He pretended not to hear him. " _Sans!"_

"What?" Sans looked down at his brother. Papyrus's eyes were full of hope.

"Do the trick." He begged. Sans made a loud, fake groan. Gaster looked up long enough to give Sans a look. He went back to his notes just as Sans light up his left eye. Papyrus clapped with excitement.

"Sans." Gaster looked at him. The bright blueish green color faded. "Since Alphys and I are meeting with the King today, you and papyrus will be free to wander the Capital. You will go no farther than Hotland. I will give you two money for lunch, so make sure you keep an eye on Papyrus." The boat stopped, and the boys followed Gaster to New Home.

Papyrus loved it there. He loved playing in the yellow flowers, and meeting all the monsters who lived and worked there. Sans would just follow him around, making sure he didn't get into too much trouble.

Today, though, Papyrus seemed set on Hotland. He wanted to explore the volcanic area that would one day power the still unfinished Core.

"Is daddy ever going to be done?" Papyrus asked. Sans looked at his little brother. He was so damn smart for his age.

"I don't know, bro. It's hard to tell. That orb project has Dad all kinds of wrapped up, but I think he'll finish the Core soon." Sans smiled at Papyrus, who looked back out into the sea of lava.

Gaster didn't know who told him, but he knew that there was a human unground. He was running through New Home, shouting for his sons.

Sans smelled the fire before he saw the human. He and Papyrus, the latter of whom was hungry, went looking to find the food. There they saw a strange looking being. Sans knew what they were immediately.

He grabbed Papyrus, but not before he shouted hello. The boy looked up at them, and smiled warmly.

"Well, howdy!" He said. The fire was blazing underneath his pan. The stained apron around his neck threw Sans, whose eyes was glowing in fear. "Just cooking up some lunch, friends. Care to join? Meals are always better with company." Papyrus got away from Sans, and walked over to the human, sitting down near him.

"I'm The Great Papyrus!" He announced. Sans approached cautiously. "What's your name?"

"I'm Jack. The Chef." He rubbed Papyrus' head. Sans sat down, and pulled his brother closer to him. "I guess you monsters don't get many humans down here, huh?"

"Nope! You seem nice though." Papyrus took a deep sniff from the pan. "Wowie! That smells really good!"

"Sans!" Gaster yelled. "Papyrus!" The boys looked up, and saw their father running towards them. Jack the Chef jumped backwards, looking thoroughly scared. Sans drug Papyrus towards Gaster, who shielded them behind him. "Are you alright?" He asked, looking back at the boys. Sans nodded.

"Daddy, Jack is nice! He was making lunch!" Papyrus quipped helpfully. Jack nodded.

Gaster eyed the human, and grabbed his arm. "Sans, I want you and papyrus to go home."

"Daddy!" Papyrus tried to but in.

"Trust me. It's for the best." Gaster explained to papyrus. The baby bones nodded, and Sans left for the River Person's boat. Gaster waited until he knew they were out of earshot. "I wish you hadn't fallen down here, human."

Sans and Papyrus made it home without any more fuss. Papyrus kept wondering when he'd get to see Jack The Chef again. Sans didn't answer. He couldn't. He was old enough to know that the King didn't let the humans live. He took their souls, and waited.

That's what the Core was supposed to prevent.

Gaster came home a few hours later, looking sullen. He smiled sadly as Papyrus enquired about his new friend.

"King Asgore will take good care of Jack, Papyrus." He lied. Papyrus seemed cont4ent wit that answer. "He's going to help us get out of the Underground."

"Good! Then Jack and I can be friends above ground!" Papyrus skipped off to his room.

"If only…" Gaster sank into the couch. Sans hadn't seen something like this, well ever. He made a cup of tea, and gingerly pressed it into his dad's hands. "Thank you, son."

"Dad… What about the core?" Sans asked. Gaster sipped the tea for a few minutes.

"Alphys and I will be returning to work on it tomorrow. You're a very smart boy." Gaster looked him up and down. "Would you like to help me?"

For the first few months it was great. Sans was able to learn to use his powers better, and he got to help out in something his dad was working on. Until Papyrus became curious.

Sans had to stop helping with the Core so that Papyrus wouldn't get hurt. Even though when Sans was five, he had been allowed to run around by himself. Chasing Papyrus was fun, but he'd much rather be working on the core.

More time passed. Papyrus didn't understand why Gaster was spending less and less time with them, so every moment he was actually home, Papyrus was all over his father. He entertained his youngest son, though Sans eventually left school. He didn't need it anyway.

Gaster began to be gone for days at a time. Papyrus would wait, every day saying he'd be back tonight for sure. When he did come home, all Gaster did was eat and sleep. A few times he'd have a screaming match with Sans, but Papyrus never got involved. Except for one.

"It's not my fault you never leave us any money!" Sans shouted. Gaster had been scolding him for the lack of food. "At least I make sure Pap is fed."

"You need to be more responsible with what I do give you." Gaster snapped back.

"You're gone for weeks! Sixty Gold doesn't fill the fridge for three weeks, Dad!"

"Please stop!" Papyrus shouted, jumping between them. Gaster swung.


End file.
